CHKDSK /R /F:
Run CHKDSK /R /F from an elevated (Run as adminstrator) Command Prompt. Please do this for each hard drive on your system.
When it tells you it can't do it right now - and asks you if you'd like to do it at the next reboot - answer Y (for Yes) and press Enter. Then reboot and let the test run. It may take a while for it to run, but keep an occasional eye on it to see if it generates any errors. See "CHKDSK LogFile" below in order to check the results of the test.
Elevated Command Prompt:
Go to Start and type in "cmd.exe" (without the quotes)
At the top of the Search Box, right click on Cmd.exe and select "Run as administrator"
Go to Start and type in "eventvwr.msc" (without the quotes) and press Enter
Expand the Windows logs heading, then select the Application log file entry.
Double click on the Source column header.
Scroll down the list until you find the Chkdsk entry (wininit for Win7) (winlogon for XP).
Copy/paste the results into your next post.